Ecologically Active - Institution of Civil Engineers

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from the experiment with H. fuscescens larvae (Fig. 8C). Although Portland showed lowest average than the ecologically active matrices, due to high variability in the results this was not supported by the statistical test. Nonetheless, pair-wide comparisons did find a marginally significant difference between M5 and Portland cement (P=0.067). The experiment with B. neritina larvae however did yield significant results (Fig. 8C, df=4, pseudo f=4.05 P=0.009), where Portland cement had lowest settlement rates (2.35±1.25% attachment), while M1 and the highest recruitment rates (14.14±7.20%). Note that M5 results were not included here as due to a technical error M5 was not included in the experiment. Figure 8: Comparison of A) natural attachment of D. hemprichi fragments, B) settlement of H. fuscescens larvae, and C) settlement of B. neritina larvae onto innovative concrete matrices in comparison to Portland cement. Discussion With global predictions of increased growth in coastal populations, the trends of coastal hardening and expansion of coastal cities is expected to further increase. Moreover, in light of processes related to global climate change, coastlines are facing growing threats related to sea-level rise and increased storminess (Dugan et al., 2011 and references therein), calling for immediate revision of current coastal defense measures. This work examines an innovative approach of applying slight modifications to the composition and surface texture of concrete, aimed at facilitating marine grow and encouraging enhanced biogenic buildup. Three of the five matrices tested (MI, M4 and M5) were found to be ecologically active, exhibiting enhanced recruitment capabilities in comparison to standard Portland cement. This was evident from most of the biological parameters examined in the lab and at the field, at both sampling stations. Overall, these ecologically active matrices recruited greater live cover (Fig. 1), more inorganic matter (Fig. 5), and had higher settlement rates of corals and target organisms (Figs. 7-8) than the standard Portland cement based mix. Enhanced recruitment capabilities of natural assemblages of marine flora and fauna onto concrete based CMI yields valuable structural, environmental and socio-economic advantages. In terms of structural advantages, as CMI are often used for coastal defense (e.g., breakwaters and seawalls), weight and stability plays a major role in structural performance. In this study, ecologically active concrete matrices accumulated significantly more inorganic matter than Portland cement. Biogenic buildup of ecosystem engineers like oysters, serpulid worms, barnacles and corals, increases the structures’ weight, contributing to its stability and strength (Risinger, 2012). According our results, an average of 413 (Med Sea) – 201 (Red Sea) gr/m 2 can be added to ecologically active concrete surfaces within a 12 m period, reaching maximal values of 1 kg/m 2 in the Med Sea and nearly 0.5 kg/m 2 in the Red Sea. While there are cases where growth of marine organisms, mainly burrowing sponges or certain species of green algae, can deteriorate concrete surfaces (Jayakumar and Saravanane, 2010, Scott et al., 1988), our results indicated of beneficial bio-protective effects. In addition to contributing to the overall weight of CMI, biogenic growth of coralline algae, oysters, corals and serpulid worms can strengthen concrete surface. For example, Risinger (2012) who examined the influence of oyster growth on concrete strength found that concrete covered with marine growth showed a significant ten-fold increase in flexural strength over a two years period. Apart from weight addition, biogenic buildup also increases the bond between adjacent infrastructure elements (armoring units, seawall precast elements, etc.), as marine growth acts as biogenic glue that can help absorb wave energy and reduce surge impact of the structure. Such biogenic buildup, which with time can cover the surface with a
calcitic layer (Fig. 9), also adds to the durability of the structure by absorbing hydrodynamic forces and protecting the concrete from chloride attacks and chipping. Although such intense growth might disrupt visual surveys of the infrastructures’ state, inspection can be achieved by scraping off sections of the growth at random (typically, no more than 10% of the surface), which will re-grow with time. In light of the above, application of ecologically active concrete matrices in CMI can help make them more sustainable, and in the long term might reduce the need and cost of maintenance work. Figure 9: Scrapped material composed of calcitic biogenic growth accumulated onto an M4 tile 3 month post deployment. Apart from structural advantages, ecologically active concrete matrices are also associated with substantial environmental benefits. As evident from the results, matrices that have proved ecologically active had significantly higher live cover than standard Portland cement (average cover of MI, M4 and M5 tiles was nearly 100% in both stations 12 months post deployment, while Portland tiles averaged 82% - 92%). Much of the live cover consisted of ecosystem engineers that contribute to biogenic buildup (oysters, corals, barnacles and serpulid worms) on one hand, and filter feeding organisms that can elevate water quality and clarity on the other (e.g., tunicates, sponges, oysters and mussels). Moreover, as evident from both the in-situ and in vitro settlement experiments, corals and other typical intertidal organisms such as B. neritina showed clear preference to ecologically active matrices, predominantly M1 and M5. Creating CMI with enhanced ability to recruit corals and species that provide valuable ecosystem services such as filter feeders and biogenic builders is of great ecological importance. By enhancing the biological productivity and ecological value of CMI we can reduce their ecological footprint and utilize them as urban nature zones, instead of viewing them as scarified “urbanized-industrial deserts”. Another environmental advantage of some of the innovative concrete matrices tested is reduced carbon footprint. As matrices include various additives that can significantly reduce the amount of Portland cement in the mix, which is known for its high carbon footprint (Matthews et al., 2008), such matrices can be considered more ecological. For example, M2 and M3 did not perform much differently from standard Portland cement under the given time frame, yet as they have a reduced carbon footprint, they can still be considered more ecological than standard concrete mixes. Nonetheless, evaluating the carbon footprint of the various concrete matrices was not the scope of the current research and requires further investigation. Finally, as CMI are an integral part of waterfronts throughout the globe, we cannot ignore their socio-economic implications. Nowadays, when environmental awareness is in constant rise, environmental agencies are calling for ecological compensation (Puig and Villarroya, 2013) and mitigation policies. Sustainable “green-blue” marine construction technologies can provide an efficient tool for managers and policy makers, reducing the environmental footprint of CMI. On top of this, integrating complex textures and designs to CMI, which promotes natural marine assemblages, also promote enhanced esthetic qualities that create urban
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Ecologically Active - Institution of Civil Engineers

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